Zero-field-cooled and field-cooled magnetization data in single-crystalline Nd0.5 Sr0.5 Mn O3 revealed the existence of thermodynamic irreversibility below Curie temperature (TC), indicating the presence of frustration of spins. The imaginary part of ac susceptibility (X″) indicates a prominent cusp below TC, which shifts to higher temperatures with increasing frequency. Magnetization, ac susceptibility, resistivity, and specific-heat measurements were used to find three critical exponents α=0.12 (1), Β=0.5 (0), and γ=1.02 (2). The values of the critical exponents are all between mean-field values and three-dimensional Heisenberg model values. © 2006 American Institute of Physics.